Java ArrayBlockingQueue toArray()用法及代码示例

1. toArray()方法ArrayBlockingQueue类：
   ArrayBlockingQueue类的toArray()方法用于按适当顺序创建一个数组，该数组包含与此ArrayBlockingQueue相同的元素。本质上，它将所有元素从ArrayBlockingQueue复制到新数组。此方法充当数组和集合之间的桥梁。

   用法:

   public Object[] toArray()

   返回值：该方法返回一个包含此队列中所有元素的数组。

   
   

   下面的程序说明ArrayBlockingQueue类的toArray()方法：
   示例1:

   // Program Demonstrate how to apply toArray() method 
   // of ArrayBlockingQueue Class. 
     
   import java.util.concurrent.ArrayBlockingQueue; 
     
   public class GFG { 
     
       public static void main(String[] args) 
       { 
           // Define capacity of ArrayBlockingQueue 
           int capacity = 5; 
     
           // Create object of ArrayBlockingQueue 
           ArrayBlockingQueue<Integer> queue = new 
                        ArrayBlockingQueue<Integer>(capacity); 
     
           // Add 5 elements to ArrayBlockingQueue 
           queue.offer(423); 
           queue.offer(422); 
           queue.offer(421); 
           queue.offer(420); 
           queue.offer(424); 
     
           // Create a array by calling toArray() method 
           Object[] array = queue.toArray(); 
     
           // Print queue 
           System.out.println("Queue is " + queue); 
     
           // Print elements of array 
           System.out.println("The array created by toArray() is:"); 
           for (Object i : array) { 
               System.out.println(i); 
           } 
       } 
   }

   输出：

   Queue is [423, 422, 421, 420, 424]
   The array created by toArray() is:
   423
   422
   421
   420
   424
   

   示例2:

   // Program Demonstrate how to apply toArray() method 
   // of ArrayBlockingQueue Class. 
     
   import java.util.concurrent.ArrayBlockingQueue; 
     
   public class GFG { 
     
       public static void main(String[] args) 
       { 
           // Define capacity of ArrayBlockingQueue 
           int capacity = 5; 
     
           // Create object of ArrayBlockingQueue 
           ArrayBlockingQueue<String> queue = new 
                         ArrayBlockingQueue<String>(capacity); 
     
           // Add 5 elements to ArrayBlockingQueue 
           queue.offer("User"); 
           queue.offer("Employee"); 
           queue.offer("Manager"); 
           queue.offer("Analyst"); 
           queue.offer("HR"); 
     
           // Create a array by calling toArray() method 
           Object[] array = queue.toArray(); 
     
           // Print queue 
           System.out.println("Queue is " + queue); 
     
           // Print elements of array 
           System.out.println("The array created by toArray() is:"); 
           for (Object i : array) { 
               System.out.println(i); 
           } 
       } 
   }

   输出：

   Queue is [User, Employee, Manager, Analyst, HR]
   The array created by toArray() is:
   User
   Employee
   Manager
   Analyst
   HR
   

2. toArray(T [] arr) 方法ArrayBlockingQueue类：
   ArrayBlockingQueue类的toArray(T [] a)方法用于创建一个数组，该数组包含与该ArrayBlockingQueue相同的元素，并且顺序正确。它有一个附加条件。如果队列大小小于或等于指定的数组，则返回的数组的类型与参数中指定的数组的类型相同。否则，将分配一个与指定数组相同类型的新数组，并且该数组的大小等于此队列的大小。此方法充当数组和集合之间的桥梁。
   假设队列是ArrayBlockingQueue，并且仅包含字符串。然后

   String[] new_arr = queue.toArray(new String[0]);

   请注意，toArray(new Object [0])与toArray()方法相同。

   用法:

   public  T[] toArray(T[] a)

   参数：该方法采用一个参数arr，该参数是一个数组，队列中的所有元素(如果足够大)都将复制到该数组中；否则，将为其分配相同运行时类型的新数组。

   返回值：该方法返回一个包含此队列中所有元素的数组。

   异常：该方法可以引发以下异常之一：

   • ArrayStoreException：当传递的数组具有不同类型并且不能与队列中的元素进行比较时。
   • NullPointerException ：如果数组为Null。

   下面的程序说明ArrayBlockingQueue类的toArray(T [] a)方法：
   示例1:

   // Program Demonstrate how to apply toArray(T[] a) method 
   // of ArrayBlockingQueue Class. 
     
   import java.util.concurrent.ArrayBlockingQueue; 
     
   public class GFG { 
     
       public static void main(String[] args) 
       { 
           // Define capacity of ArrayBlockingQueue 
           int capacity = 5; 
     
           // Create object of ArrayBlockingQueue 
           ArrayBlockingQueue<String> queue = new 
                    ArrayBlockingQueue<String>(capacity); 
     
           // Add 5 elements to ArrayBlockingQueue 
           queue.offer("User"); 
           queue.offer("Employee"); 
           queue.offer("Manager"); 
           queue.offer("Analyst"); 
           queue.offer("HR"); 
     
           // Creating the array 
           String[] array = new String[5]; 
     
           // Calling toArray(T[] a) method 
           Object[] ReturnArray = queue.toArray(array); 
     
           // Print queue 
           System.out.println("Queue is " + queue); 
     
           // Print elements of array passed as parameter 
           System.out.println(); 
           System.out.println("The array passed to toArray() is:"); 
           for (Object i : array) { 
               System.out.println(i); 
           } 
     
           // Print elements of array retuned by method toArray() 
           System.out.println(); 
           System.out.println("The array retuned by toArray() is:"); 
           for (Object i : ReturnArray) { 
               System.out.println(i); 
           } 
       } 
   }

   输出：

   Queue is [User, Employee, Manager, Analyst, HR]
   
   The array passed to toArray() is:
   User
   Employee
   Manager
   Analyst
   HR
   
   The array retuned by toArray() is:
   User
   Employee
   Manager
   Analyst
   HR
   

参考：

• https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ArrayBlockingQueue.html#toArray
• https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/ArrayBlockingQueue.html#toArray-T:A